How CAC Payback Period Calculator works

1. Scope

The CAC Payback Calculator reports how many months of gross profit per customer are needed to recover the cost of acquiring that customer. It is the margin-adjusted version of the payback formula — the one relevant to capital-efficiency decisions. It operates at the aggregate level; cohort-level payback is more accurate but requires per-customer timestamps the tool does not ingest.

2. Inputs and outputs

Inputs: CAC (blended acquisition cost per paying customer), ARPU, gross margin, monthly churn rate. Outputs: payback in months, LTV (gross-profit form), LTV:CAC ratio, and a health band benchmarked against published SaaS percentiles.

Engine source: src/lib/cac-payback-calculator/engine.ts.

3. Formula / scoring logic

payback_months  = CAC / (ARPU * gross_margin)
LTV             = (ARPU * gross_margin) / monthly_churn
LTV_CAC_ratio   = LTV / CAC

The gross-margin multiplier in the denominator is load-bearing. Without it, payback is "months until CAC is recovered in gross revenue," which ignores cost-to-serve and systematically understates the recovery horizon. Include it unless the business is software-margin-trivial (e.g. infrastructure-light information products where gross margin is ≈ 100%).

4. Assumptions

• Aggregate, not cohort. Blended CAC hides the fact that organic and paid customers have vastly different payback profiles. Segment explicitly if the mix is meaningful.
• Memoryless churn. LTV formula uses the same constant-churn assumption as elsewhere on this site.
• Gross margin is customer-variable-cost margin. Payment-processing, inference, hosting, fulfilment. Excludes overhead.
• ARPU is the price the customer actually pays. Annual plans should be normalised to monthly equivalent.
• CAC is fully-loaded. Sales salaries, ad spend, tooling, attributable content investment.

5. Data sources

• OpenView SaaS Benchmarks 2024 — CAC payback percentiles by stage and GTM motion (12-month median for mature B2B SaaS; higher for early-stage or long-sales-cycle enterprise).
• SaaS Capital Annual Survey — bootstrapped and capital-efficient payback percentiles.
• Paddle SaaS Benchmarks 2024 — B2B vs B2C norms.

6. Known limitations

• Aggregate blending is misleading when the mix is asymmetric. If 70% of acquisition is organic (near-zero CAC) and 30% is paid (high CAC), the aggregate payback number reflects neither channel's economics.
• Cohort-level payback requires data the tool does not ingest. Cohort payback is the fraction of CAC recovered from gross profit generated by the specific cohort up to month m. Computing it needs per-customer signup and gross-profit timestamps.
• 12-month payback is a rule of thumb, not a law. Benchmarks vary by stage: top-quartile bootstrapped SaaS often clears payback in 3–6 months; enterprise SaaS routinely runs 18–24 months.
• Margin timing is ignored. Annual plans have payback denominated in months of revenue but collected upfront. A more accurate cash-payback would discount future months by a cost-of-capital rate — this tool reports nominal payback.

7. Reproducibility

8. Change log

• 2026-04-24methodology page first published. Gross-margin-adjusted payback and LTV:CAC documented, with cohort-vs-aggregate caveat.